Conventionally, indexable milling cutters as described in the following Patent Literatures 1 and 2, for example, are known. Such an indexable milling center includes a tool body that is configured to rotate about an axis, a plurality of insert attachment seats that are formed at an outer peripheral part of a tip with intervals provided between one another in a circumferential direction, and cutting inserts that are respectively detachably attached to these insert attachment seats.
In addition, front edges (flat face machining cutting edges) for working a flat face in a working material are provided on the cutting inserts. The front edges are arranged to conform to a virtual plane that is perpendicular to the axis of the tool body when the cutting inserts are attached to the insert attachment seats. The machined surface of the work material, on which a milling has been performed by the front edges of the cutting inserts is finished as a smooth flat face.
Note that the indexable milling cutters described in Patent Literatures 1 and 2 are provided with adjustment mechanisms capable of adjusting the positions of the cutting inserts attached to the insert attachment seat in the axial direction. The adjustment mechanisms adjust the respective front edges of the plurality of cutting inserts such that they become positioned on one virtual plane that is perpendicular to the axis.
Incidentally, in a structure in which mating faces (flat faces formed into annular shapes along openings of case bodies) of a pair of case bodies are abutted to each other and are combined, such as a clutch housing or a transmission case for a vehicle, for example, a milling is performed in advance on the mating faces by milling cutter such as the aforementioned indexable milling cutter to form the faces into flat faces. Also, a sealing agent such as a liquid packing is interposed between these mating faces, thereby securing a sealing property.
It is preferable to apply surface roughness in a predetermined range, in which irregularities are formed to some extent rather than to form the mating faces as smooth flat faces, in order to maintain the sealing agent in the mating faces stably. That is, since a contact area with the sealing agent increases, a holding property of the sealing agent increases, a sealing effect becomes stable, and leakage or the like of the sealing agent due to vibration or the like tends not to occur due to the minute irregularities formed on the mating faces. Specifically, there may be a case in which not too fine and not too rough surface roughness (surface roughness that falls between a predetermined upper limit value and a lower limit value), for example, surface roughness in a predetermined range of Rz (10-point average roughness) of about several μm to several tens of μm is required for the surface roughness of a work material.
In order to realize such surface roughness in the related art, it is necessary to obtain mating faces (machined surfaces) with prescribed surface roughness by working a work material to obtain smooth flat faces first by using an indexable milling cutter and then appropriately scratching and damaging the flat faces by using a grindstone or the like in another process.